Recently, the scanning tunneling microscope (STM) has been developed as an apparatus capable of observing the surface structure of a substance surface at an atomic order resolution.
The measuring principle of the scanning tunneling microscope is described below.
On the sample surface to be measured, a probe made of an extremely sharp pointed metal tip is brought within a distance of about 10 angsttoms, and a bias voltage of about 10 mV to 2 V is applied between the sample and the probe, and then a tunneling current of several nA flows. The tunneling current is very sensitive to the distance between the sample and probe, and this distance may be kept constant by employing the feedback control.
The probe is attached to an actuator composed of a piezoelectric element capable of inching in three axial directions of X, Y, Z. By relatively moving sample and probe in the X-Y direction in raster scan, the distance between the sample and probe is kept constant by the feedback control of the Z direction, while the change of voltage applied to the position control of the Z direction directly expresses the topography of the sample surface.
Such scanning tunneling microscope technology has produced, peripheral technologies such as the atomic force microscope (AFM), near field optical microscope (NFOM), other observation apparatuses, and ultrahigh-precision processing machines capable of manipulating atoms and molecules. These technologies commonly possess the means of scanning the sample surface while maintaining an atomic order distance between the sample and probe, and including their observation apparatuses, they are commonly called a near field microscope (NFM) or a scanning probe microscope (SPM).
In order to scan while maintaining the atomic order distance between the probe and sample, it is of prime importance that mechanical vibrations affecting distance fluctuations should be thoroughly eliminated. And in the positioning device of the invention, it is also required that this be the first condition.
In addition, in the analysis of a semiconductor element, or analysis of a superlattice quantum effect device, when applying the scanning tunneling microscope, the positioning mechanism is needed to search for a specific position on the sample. Furthermore, in a ultrahigh-precision processing machine utilizing the scanning tunneling microscopic technology, a highly accurate positioning device for controlling X-Y position coordinates is needed.
As an example of a simple positioning function for the scanning tunneling microscope of the type for use in an air atmosphere without installing a specific positioning device, the probe head mounting the scanning probe is manually moved while observing the sample and scanning probe from an oblique direction by an optical microscope.
Moreover, in an example of a positioning device for the scanning tunneling microscope of the type for use in a vacuum, the sample was positioned by a driving device while observing the sample and the scanning probe from an oblique direction by a scanning electron microscope (SEM).
In the conventional scanning tunneling microscope, however high in precision the absolute positioning function of the X-Y position coordinates of the sample and scanning probe may be, so far as the mechanical vibrations cannot be eliminated completely, it is not sufficient for accurate X-Y positioning.
When scanning at a distance of an atomic order from the scanning probe to the sample, the mechanical vibrations affecting the fluctuations of the distance must be thoroughly eliminated, and in the conventional positioning device, it is difficult to satisfy both vibration control and accurate X-Y positioning at the same time. Actually, the above-mentioned conventional SEM or STM does not have any function for precisely and absolutely positioning the X-Y position coordinates.